Passive water management fuel cell

Abstract

A proton exchange membrane (PEM) fuel cell includes fuel and oxidant flow field plates ( 26, 40 ) having fuel and oxidant channels ( 27, 28; 41, 44 ), and water channels, the ends ( 29, 48 ) of which that are adjacent to the corresponding reactant gas inlet manifold ( 34, 42 ) are dead ended, the other ends ( 31, 50 ) draining excess water into the corresponding reactant gas exhaust manifold ( 36, 45 ). Flow restrictors ( 39, 47 ) maintain reactant gas pressure above exit manifold pressure, and may comprise interdigitated channels ( 65, 66; 76, 78 ). Solid reactant gas flow field plates have small holes ( 85, 88 ) between reactant gas channels ( 27, 28; 41 ) and water drain channels ( 29, 30; 49, 50 ). In one embodiment, the fuel cells of a stack may be separated by either coolant plates ( 51 ) or solid plates ( 55 ) or both. In a second embodiment, coolant plates ( 51 a ) have weep holes ( 57 ) that inject water into the ends ( 29 ) of the reactant gas water channels which are in the region of the inlet manifold ( 34 ), thereby assuring humidification of the reactants.

We claim:  
     
       1. A fuel cell comprising: 
       an anode substrate and a cathode substrate and a proton exchange membrane disposed between said substrates;  
       an anode flow field plate providing a fuel reactant gas flow field adjacent said anode substrate;  
       a cathode flow field plate providing an oxidant reactant gas flow field adjacent said cathode substrate;  
       said fuel reactant gas flow field receiving fuel from a fuel reactant gas inlet manifold and exhausting into a fuel reactant gas exhaust manifold;  
       said oxidant reactant gas flow field receiving oxidant from an oxidant reactant gas inlet manifold and exhausting into an oxidant reactant gas exit manifold; and  
       at least one of said flow field plates being porous and having a water flow field on a side of said at least one of said flow field plates opposite the corresponding one of said reactant gas flow fields, said water flow field being dead ended in the region of the corresponding one of said reactant gas inlet manifolds and opening into the corresponding one of said reactant gas exit manifolds, and having a flow restrictor at the exhaust end thereof to maintain the pressure of reactant gas in said one flow reactant gas field above the pressure of reactant gas in said corresponding one of said reactant gas exit manifolds.  
     
     
       2. A fuel cell stack comprising: 
       a plurality of fuel cells according to  claim 1 ;  
       and a gas impervious separator plate separating each of said fuel cells from adjacent ones of said fuel cells, said separator plate selected from (a) a cooling plate having a coolant flow field therein and (b) a solid plate.  
     
     
       3. Fuel cell according to  claim 1  wherein: 
       said flow restrictor maintains the pressure of reactant gas between 0.2 and 2.0 psi above the pressure in the corresponding exit manifold.  
     
     
       4. A fuel cell stack comprising: 
       a plurality of fuel cells according to  claim 1 ;  
       a plurality of cooling plates, each having a coolant flow field therein, each of said fuel cells being separated from a fuel cell adjacent thereto by one of said cooling plates, a portion of each of said coolant flow fields coaligned with a portion of at least one of said reactant flow fields in the vicinity of said reactant gas inlet manifold, there being at least one weep hole between said portion of each said coolant flow field and the one of said reactant gas flow fields coalianed therewith.  
     
     
       5. A fuel cell according to  claim 1  wherein: said flow restrictor comprises interdigitated reactant gas flow field channels. 
     
     
       6. A fuel cell according to  claim 1  wherein: 
       at least one of said substrates is porous and is selected from (a) a hydrophilic substrate, (b) a wetproofed substrate, and c) a substrate which is partially hydrophilic and partially wetproofed.  
     
     
       7. A fuel cell according to  claim 1  wherein: 
       at least one of said flow field plates is solid with reactant gas flow channels and small holes extending from said channels into said water flow field.  
     
     
       8. A fuel cell according to  claim 7  wherein: 
       said small holes are filled with a particulate material thereby forming a porous plug.